Research findings in the past year on this continuation grant have shown that subtle differences in hemispheric organization may exist in normal left-handed adults. These differences, while still unclear and not always consistent, are compatible with some clinical studies which reveal a higher incidence and remission from aphasia in left-handed adults following unilateral brain injury. While these data suggest that hemispheric speech lateralization is less complete in left-handers, our results still indicate an asymmetric hemisphere organization of language. However, the claim that this atypical organization confers a disadvantage on right-hemisphere perceptual-spatial abilities is not supported by our studies, neither for children nor for adults. Spatial abilities are similar for both left- and right-handers. However, deficient spatial ability may occur as a function of atypical cerebral lateralization, in normal Ss, independent of handedness. This problem is being investigated. Results also show no increased prevalence of left-handedness in dyslexic children, nor in other disorders of reading and writing. This is felt to be due to unilateral brain-injury (left hemisphere) not demonstrated in cases of dyslexia. The results of our developmental work also fail to show any differences in cerebral speech lateralization between right-handed dyslexic and control readers. However, such differences were found between left- and right-handed average readers (ages five and eight) in our longitudinal project. BIBLIOGRAPHIC REFERENCES: Hines, D., Sutker, L., Satz, P. and Altman, A. Recall of letters from the left and right visual half-fields under unilateral and bilateral presentation. Perceptual and Motor Skills, 1976 42, 531-539. Satz, P., Taylor, G., Friel, J. and Fletcher, J. Some predictive and developmental precursors of reading disability: A six-year follow-up. In D. Pearl, et. al. (Eds.), Dyslexia: A critical appraisal of current theory, 1977, in press.